This invention relates to recording cartridge containing flexible magnetic recording discs and in particular to a recording cartridge having a smoothing plane surface above which the disc rotates during system operation.
In recording or reading information on a moving information storage media, such as a magnetic recording disc, relative motion between a magnetic head transducer used for reading and writing information and the storage media on which information is written on and read from is required. The relative velocity between the head and media interface may be, for example, 550 IPS for video and high density digital applications. To achieve maximum performance, there must be an interface of intimate contact between the head and media surface without destruction or excessive wear of the magnetic flux responsive coating on the surface.
As contact pressure between the head and media is increased to improve performance, both media and head wear are increased. The problem is particularly severe in video applications and compounded with the medias utilized for storing single video frames on separate tracks of a magnetic disc wherein one track at a time is continuously in contact with the head to provide a continuous stationary display of a single frame. In only five minutes of playtime revolving at 3600 RPM, for example, a track on the disc is scraped about 18,000 times by the head; the wear by-products are so hard and abrasive that the same materials are commonly used as lapping compounds.
To prevent failure caused by contact between the head and disc, lubricated surfaces and/or air film separations have been used. However, any separation between the head and disc caused by such lubrication fluid or air film imposes a loss of signal and hence performance. A head/disc separation equal to one wave length could cause about 54.6 dB loss in the output of the replay head. Since it is desired to record wave lengths that approach 1.75 microns, the playback head voltage is reduced to 50% by only 0.19 micron of separation. On the other hand, as disscussed above, reduction of separation to meet desired performance would cause the interface to be destroyed within a few seconds.
Prior art solutions to the head-to-disc interface problem have generally been of two types: flying heads in conjunction with rigid hard-plated discs and heads having large surface areas buried in soft flexible "floppy" discs. Flying head discs are very expensive and require complicated and expensive recording/playback systems. A flexible or so-called "floppy" disc reduces the handling and cost problems incurred in the flying head rigid-disc system. Some record/read heads for "floppy" discs are relatively large to provide an interface comprised of a large contoured head buried in the soft flexible media. The large record/read head surface area distributes the force per unit area to reduce media wear and separation loss. As the media is moved past the head, however, air collects between the head and disc surface to form an air film. The thickness of this air film is a function of media tension, head surface radius, viscosity of the air and disc-head relative velocity. Because of these restraints, most flexible or "floppy" disc applications are limited to slow speed, low bandwidth digital computer applications or voice recording systems.
Systems with the flexible magnetic recording disc which is separated from the recording/playback head by a thin film of air are known in the art. When the head is maintained in close proximity to the disc, but not in contact therewith, effective transfer of the information signal is achieved while at the same time minimizing wear. When a thin cartridge configuration having a flat smoothing plane surface is used, vertical head penetrations as little as 4 mils (0.11 mm) may cause the disc to "fly away" from the head, thus destroying the head-to-disc interface that is necessary for effective system operation. The thin cartridge configuration, while convenient to use, does not provide enough stability for the disc to tolerate vertical head movements. Therefore, system tolerances are critical, which greatly complicates the manufacturing process.
The use of a curved smoothing plane, as described and claimed in U.S. Pat. No. 4,063,295, gives the disc added stability and prevents it from flying away from the head, even during head penetrations of 10 mils (0.254 mm) or more. This allows greater freedom of movement of the head in a vertical plane during operation and facilitates the manufacturing process by permitting larger tolerances in the head position. Use of a curved smoothing plane, however, precludes the use of a thin flat cartridge configuration. The present invention is an improvement of the invention claimed in the aforementioned patent in that it combines the advantages of the curved smoothing plane with the advantages of a thin, flat cartridge configuration.